// Tencent is pleased to support the open source community by making RapidJSON available.
// 
// Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip. All rights reserved.
//
// Licensed under the MIT License (the "License"); you may not use this file except
// in compliance with the License. You may obtain a copy of the License at
//
// http://opensource.org/licenses/MIT
//
// Unless required by applicable law or agreed to in writing, software distributed 
// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR 
// CONDITIONS OF ANY KIND, either express or implied. See the License for the 
// specific language governing permissions and limitations under the License.

// This is a C++ header-only implementation of Grisu2 algorithm from the publication:
// Loitsch, Florian. "Printing floating-point numbers quickly and accurately with
// integers." ACM Sigplan Notices 45.6 (2010): 233-243.

#ifndef RAPIDJSON_DTOA_
#define RAPIDJSON_DTOA_

#include "itoa.h" // GetDigitsLut()
#include "diyfp.h"
#include "ieee754.h"

RAPIDJSON_NAMESPACE_BEGIN
    namespace internal {

#ifdef __GNUC__
        RAPIDJSON_DIAG_PUSH
        RAPIDJSON_DIAG_OFF(effc++)
        RAPIDJSON_DIAG_OFF(array -
                           bounds) // some gcc versions generate wrong warnings https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59124
#endif

        inline void
        GrisuRound(char *buffer, int len, uint64_t delta, uint64_t rest, uint64_t ten_kappa, uint64_t wp_w) {
            while (rest < wp_w && delta - rest >= ten_kappa &&
                   (rest + ten_kappa < wp_w ||  /// closer
                    wp_w - rest > rest + ten_kappa - wp_w)) {
                buffer[len - 1]--;
                rest += ten_kappa;
            }
        }

        inline unsigned CountDecimalDigit32(uint32_t n) {
            // Simple pure C++ implementation was faster than __builtin_clz version in this situation.
            if (n < 10) return 1;
            if (n < 100) return 2;
            if (n < 1000) return 3;
            if (n < 10000) return 4;
            if (n < 100000) return 5;
            if (n < 1000000) return 6;
            if (n < 10000000) return 7;
            if (n < 100000000) return 8;
            // Will not reach 10 digits in DigitGen()
            //if (n < 1000000000) return 9;
            //return 10;
            return 9;
        }

        inline void DigitGen(const DiyFp &W, const DiyFp &Mp, uint64_t delta, char *buffer, int *len, int *K) {
            static const uint32_t kPow10[] = {1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000,
                                              1000000000};
            const DiyFp one(uint64_t(1) << -Mp.e, Mp.e);
            const DiyFp wp_w = Mp - W;
            uint32_t p1 = static_cast<uint32_t>(Mp.f >> -one.e);
            uint64_t p2 = Mp.f & (one.f - 1);
            unsigned kappa = CountDecimalDigit32(p1); // kappa in [0, 9]
            *len = 0;

            while (kappa > 0) {
                uint32_t d = 0;
                switch (kappa) {
                    case 9:
                        d = p1 / 100000000;
                        p1 %= 100000000;
                        break;
                    case 8:
                        d = p1 / 10000000;
                        p1 %= 10000000;
                        break;
                    case 7:
                        d = p1 / 1000000;
                        p1 %= 1000000;
                        break;
                    case 6:
                        d = p1 / 100000;
                        p1 %= 100000;
                        break;
                    case 5:
                        d = p1 / 10000;
                        p1 %= 10000;
                        break;
                    case 4:
                        d = p1 / 1000;
                        p1 %= 1000;
                        break;
                    case 3:
                        d = p1 / 100;
                        p1 %= 100;
                        break;
                    case 2:
                        d = p1 / 10;
                        p1 %= 10;
                        break;
                    case 1:
                        d = p1;
                        p1 = 0;
                        break;
                    default:;
                }
                if (d || *len)
                    buffer[(*len)++] = static_cast<char>('0' + static_cast<char>(d));
                kappa--;
                uint64_t tmp = (static_cast<uint64_t>(p1) << -one.e) + p2;
                if (tmp <= delta) {
                    *K += kappa;
                    GrisuRound(buffer, *len, delta, tmp, static_cast<uint64_t>(kPow10[kappa]) << -one.e, wp_w.f);
                    return;
                }
            }

            // kappa = 0
            for (;;) {
                p2 *= 10;
                delta *= 10;
                char d = static_cast<char>(p2 >> -one.e);
                if (d || *len)
                    buffer[(*len)++] = static_cast<char>('0' + d);
                p2 &= one.f - 1;
                kappa--;
                if (p2 < delta) {
                    *K += kappa;
                    int index = -static_cast<int>(kappa);
                    GrisuRound(buffer, *len, delta, p2, one.f,
                               wp_w.f * (index < 9 ? kPow10[-static_cast<int>(kappa)] : 0));
                    return;
                }
            }
        }

        inline void Grisu2(double value, char *buffer, int *length, int *K) {
            const DiyFp v(value);
            DiyFp w_m, w_p;
            v.NormalizedBoundaries(&w_m, &w_p);

            const DiyFp c_mk = GetCachedPower(w_p.e, K);
            const DiyFp W = v.Normalize() * c_mk;
            DiyFp Wp = w_p * c_mk;
            DiyFp Wm = w_m * c_mk;
            Wm.f++;
            Wp.f--;
            DigitGen(W, Wp, Wp.f - Wm.f, buffer, length, K);
        }

        inline char *WriteExponent(int K, char *buffer) {
            if (K < 0) {
                *buffer++ = '-';
                K = -K;
            }

            if (K >= 100) {
                *buffer++ = static_cast<char>('0' + static_cast<char>(K / 100));
                K %= 100;
                const char *d = GetDigitsLut() + K * 2;
                *buffer++ = d[0];
                *buffer++ = d[1];
            } else if (K >= 10) {
                const char *d = GetDigitsLut() + K * 2;
                *buffer++ = d[0];
                *buffer++ = d[1];
            } else
                *buffer++ = static_cast<char>('0' + static_cast<char>(K));

            return buffer;
        }

        inline char *Prettify(char *buffer, int length, int k, int maxDecimalPlaces) {
            const int kk = length + k;  // 10^(kk-1) <= v < 10^kk

            if (0 <= k && kk <= 21) {
                // 1234e7 -> 12340000000
                for (int i = length; i < kk; i++)
                    buffer[i] = '0';
                buffer[kk] = '.';
                buffer[kk + 1] = '0';
                return &buffer[kk + 2];
            } else if (0 < kk && kk <= 21) {
                // 1234e-2 -> 12.34
                std::memmove(&buffer[kk + 1], &buffer[kk], static_cast<size_t>(length - kk));
                buffer[kk] = '.';
                if (0 > k + maxDecimalPlaces) {
                    // When maxDecimalPlaces = 2, 1.2345 -> 1.23, 1.102 -> 1.1
                    // Remove extra trailing zeros (at least one) after truncation.
                    for (int i = kk + maxDecimalPlaces; i > kk + 1; i--)
                        if (buffer[i] != '0')
                            return &buffer[i + 1];
                    return &buffer[kk + 2]; // Reserve one zero
                } else
                    return &buffer[length + 1];
            } else if (-6 < kk && kk <= 0) {
                // 1234e-6 -> 0.001234
                const int offset = 2 - kk;
                std::memmove(&buffer[offset], &buffer[0], static_cast<size_t>(length));
                buffer[0] = '0';
                buffer[1] = '.';
                for (int i = 2; i < offset; i++)
                    buffer[i] = '0';
                if (length - kk > maxDecimalPlaces) {
                    // When maxDecimalPlaces = 2, 0.123 -> 0.12, 0.102 -> 0.1
                    // Remove extra trailing zeros (at least one) after truncation.
                    for (int i = maxDecimalPlaces + 1; i > 2; i--)
                        if (buffer[i] != '0')
                            return &buffer[i + 1];
                    return &buffer[3]; // Reserve one zero
                } else
                    return &buffer[length + offset];
            } else if (kk < -maxDecimalPlaces) {
                // Truncate to zero
                buffer[0] = '0';
                buffer[1] = '.';
                buffer[2] = '0';
                return &buffer[3];
            } else if (length == 1) {
                // 1e30
                buffer[1] = 'e';
                return WriteExponent(kk - 1, &buffer[2]);
            } else {
                // 1234e30 -> 1.234e33
                std::memmove(&buffer[2], &buffer[1], static_cast<size_t>(length - 1));
                buffer[1] = '.';
                buffer[length + 1] = 'e';
                return WriteExponent(kk - 1, &buffer[0 + length + 2]);
            }
        }

        inline char *dtoa(double value, char *buffer, int maxDecimalPlaces = 324) {
            RAPIDJSON_ASSERT(maxDecimalPlaces >= 1);
            Double d(value);
            if (d.IsZero()) {
                if (d.Sign())
                    *buffer++ = '-';     // -0.0, Issue #289
                buffer[0] = '0';
                buffer[1] = '.';
                buffer[2] = '0';
                return &buffer[3];
            } else {
                if (value < 0) {
                    *buffer++ = '-';
                    value = -value;
                }
                int length, K;
                Grisu2(value, buffer, &length, &K);
                return Prettify(buffer, length, K, maxDecimalPlaces);
            }
        }

#ifdef __GNUC__
        RAPIDJSON_DIAG_POP
#endif

    } // namespace internal
RAPIDJSON_NAMESPACE_END

#endif // RAPIDJSON_DTOA_
